Abstract: MEASUREMENT OF HALF LIFF OF ~(79)Se USING RADIOCHEMICAL METHODYU RUNLAN；GUO JINGRU；CUI ANZHI；TANG PEIJIA； LI DAMING；LIU DAMING（China Institute of Atomic Energy，P，O，Box 275（26），Beijing 102413）ABSTRACT~(79)Se is a long lived fission product nuclide. Scientists gradually pay attention to ~(79)Se owing toits importance in radiowaste disposal．Its half life value must be known accuratelv in order to cal-culate its content in radiowaste and the radiation dose of ~(79)Se migrated to biosphere. Up to now，however，there is no accurate value inkerature, In 1949 Parker et al．measured the half life of ~(79)Se，but they only obtained an upper limit，T_(1／2)≤6．5×10~4a，which is still used at present in nu-dear data literatureq. In the present work，the half life of ~(79)Se has been measured using radioChemical method．Ra-diochemically pure ~(79)Se is separated from irradiated ~(235)U targets and its activity is measured by aliquid scintillation spectrometer. According to its fission yield the number of’9Se nuclei is calculat-ed by means ofhsion monitors．~(137)Cs and ~(90)Sr are selected as monitors. The activitv is measuredusing HPGe γ spectrometer for ~(137)Cs and Cherenkov liquid scintillation counting for ~(90)Sr. The halflife of ~(79)Se is obtained to be（4．8±0．4）×10~5a. Key words ~(79)Se Half fife Fission monitors.